Sailboats generally comprise one or more tell-tales attached to the rigging or to certain parts of the sail. The tell-tales generally come in the form of light streamers, made of material or wool, so as to follow the flow of the wind. The tell-tales are thus commonly used by the helmsman to display the direction of the wind, and thus the flow regime, laminar or turbulent, of the flow of air on the sail. This information is used by the helmsman to set his sail in order to optimize the aerodynamic flow around the sail so as to increase the thrust of the wind in the sail and thus the speed of the sailboat.
The tell-tales generally extend from the leading edge of the sail up to the rear part of the sail. When the tell-tale extends horizontally in a uniform and stationary manner within the air flow, the flow over the sail is laminar. A laminar flow corresponds to the optimum adjustment of the sail.
Any other position of the tell-tale reflects a disrupted flow of air around the sail, i.e., a turbulent flow. Such a turbulent flow is very unstable and chaotic, which impairs the aerodynamic yield of the sail. The helmsman modifies the path of the boat and/or then corrects the setting of the sail by adjusting the sheet, the sheet traveler and/or the leech line, until a laminar flow of the air is obtained around the sail.
However, in darkness or when meteorological conditions are poor, it is no longer possible to display the tell-tales. The helmsman no longer has information on the air flow regime around the sail and therefore can no longer optimize the settings of this sail.
A solution is proposed by the document U.S. Pat. No. 5,877,415 that describes a device for detecting the flow regime of the air along a surface. This device essentially comprises a tell-tale and a disk that is mounted to rotate around a shaft, to which the tell-tale is attached. When the air flow is turbulent and moves the tell-tale, the disk pivots around its axis of rotation. The rotational movement of the disk is detected and converted into an electrical signal that is transmitted to a processing unit. The electrical signal is then displayed in such a way that the user can derive from it the degree of turbulence of the air flow and thus consequently set the sail to obtain a laminar flow.
However, this solution makes it necessary to connect the tell-tale to an element that is mounted to rotate around an axis of rotation. This element that is mounted to rotate around the axis of rotation is subjected to external attacks, such as wind and sea water; this creates the risk of impairing the rotational connection of this element. The risk of breakdown or malfunction of such a device is then significant.
Devices for determining characteristics of a fluid flow that comprise a flexible element that is equipped with a stress gauge are also known from the prior art, in particular the documents DE 3138985, EP 1158278, DE 10147090 and U.S. Pat. No. 3,696,673. Said flexible element is attached by one of its ends to a support element that is arranged in the fluid flow such that the deformations that are recorded by the stress gauge make it possible to identify the regime of the fluid flow. However, in such devices, the flexible element extends approximately perpendicularly to said support element such that the flexible element extends crosswise to the fluid flow that circulates in the vicinity of the support element and thus disrupts the air flow. Such devices are thus very intrusive in the sense that they disrupt and modify the flow whose characteristics it is desired to determine. These devices could be suitable for measuring the regime of the flow, but they do not make it possible to determine in a reliable manner the regime of the flow of fluid that circulates in the immediate vicinity of the support element of the flexible element. Such devices in which said flexible element extends through the fluid flow also run the risk of resonating, which does not make it possible to determine the characteristics of the flow itself. Thus, such devices are not only intrusive but in addition do not make it possible to reflect the flow regime of the fluid.